1. Field of the Invention
The present invention relates to the distribution of data, and, in particular, to a system and method for transferring data from one sender location to multiple receiving locations and for enabling a receiving location to recover data previously distributed when the receiving location was disabled.
2. Background of the Invention
The client-server model is a popular technique for efficiently sharing and distributing data among a network of computers. In a typical client-server system architecture, one computer acts as the “back end” or server, which performs complex tasks. Other, smaller computers or terminals act as the “front-end” or clients, which communicate with a user and typically perform other, less complex tasks. The client requests data from the server. A client is defined as a requester of services and a server is defined as the provider of services. A single machine can be both a client and a server depending on the software configuration.
FIG. 1 illustrates a client-server architecture in which a transfer server 100 receives data from a data source 102 and distributes the data to data processing clients 104. Typically, transfer server 100 distributes the data from data source 102 by transferring data files to the multiple clients 104 in separate point-to-point communications 110 using, for example, File Transfer Protocol (FTP). In turn, clients 104 read, manipulate, and analyze the data in different ways to provide network users with various forms of useful information.
As an example of this client-server data distribution, data source 102 could be the network control center (NCC) of a digital wireless packet switching network. As such, data source 102 could provide continuous performance log files including data such as network capacity, regional traffic data, and alarms indicating network areas experiencing overload conditions. Transfer server 100 would copy these performance log files to each of the clients 104, which would then analyze the data in different ways and present network users with different aspects of network performance. After viewing the network performance, a network user (e.g., a systems engineer) could then make operational adjustments to improve the performance of the digital wireless network.
In a sizeable digital wireless packet switching network, large amounts of data continuously enter the network control center. Indeed, it is not uncommon to transfer over a gigabyte of data per day, as is the case with the Mobitex digital wireless data network of BellSouth Wireless Data (Woodbridge, N.J.). Therefore, transfer server 100 must continually copy data in point-to-point FTP transfers to each of clients 104. In addition, although FIG. 1 shows only three clients 104 for simplicity, an actual digital wireless packet switching network requires numerous clients to monitor the many aspects of network performance, as is represented by the labels 1,2, . . . N of clients 104. Thus, transfer server 100 is almost continually occupied with file transfers, burdening not only its resources, but network bandwidth as well.
This method of data distribution further strains the resources of transfer server 100 when a client is unable to accept a data transfer, for example, when a client experiences a catastrophic error and crashes. In such a situation, transfer server 100 cannot copy the data to the disabled client, and instead must create a directory and store the data until the disabled client is back on line. In this manner, transfer server 100 can preserve the integrity of the analyses performed by the client by restoring the disabled client with the data that it missed while it was off line. However, in doing so, transfer server 100 must reserve considerable storage and processing capacity for responding to the disabled client's request for historical data. With one gigabyte of data processed per day, for example, transfer server 100 then risks consuming its own disk space and also crashing.
To reduce network bandwidth consumption and to ease the burden on transfer server 100, many network administrators have turned to broadcast and multicast messaging software to distribute data from a server to a group of clients. A broadcast transmission delivers a message to all clients and servers within a network, and is analogous to a radio station broadcasting audio content to a number of tuned-in radios. A multicast transmission delivers a message to a specific subset of the clients and servers within a network. As used herein, “broadcast” means to transmit a message from a single network component (e.g., a client) to all network components (e.g., clients and servers) with which the single network component is in communication. Also, as used herein, “multicast” is a form of broadcast, in which a single network component transmits a message to a group of network components, but not necessarily all network components.
As shown in FIG. 2, the broadcast and multicast approaches eliminate the repetitive point-to-point communications between transfer server 100 and clients 104. Instead, the broadcast and multicast messaging software enables server 100 to broadcast a single data transfer 200 that is received by all of the clients 104 at the same time. An example of this type of messaging software is TIB Rendezvous™ by TIBCO™ of Palo Alto, Calif. Another example of suitable messaging software is Transaction Control Protocol/Internet Protocol (TCP/IP), in which datagrams can be used to broadcast or multicast messages. In addition to broadcast and multicast messaging, these types of messaging software also support the traditional point-to-point communications.
In the example of FIG. 2, messaging software runs on transfer server 100. Correspondingly, client computers 104 run a viewer of the messaging software of server 100. Using the messaging software, server 100 can broadcast a single communication 200 to clients 1,2, . . . N of clients 104 instead of completing multiple point-to-point communications to each individual client. In addition to a broadcast, server 100 could also multicast a single message to, for example, clients 1 and 2 of clients 104, but not to client N.
Overall, this broadcast and multicast messaging technology minimizes the computing and communication responsibilities of the server. Despite serving  multiple clients, the server need only process data once and send a single message. In addition, this broadcast/multicast technique reduces network bandwidth consumption by limiting the number of transmissions.
Despite minimizing network usage and the processing responsibilities of transfer server 100, the broadcast and multicast messaging software presents problems with guaranteeing reliable data transfers to the clients. Specifically, because the broadcast transfer is point-to-multipoint, the sender (transfer server 100) does not know whether the message has been received by all of the listeners (clients 104). This condition is analogous to a radio station not being able to recognize how many radios are tuned-in, and, particularly, whether a specific radio has missed a broadcast. (A system administrator could address this problem by having clients 104 return acknowledgement messages for each received message. However, this technique would consume considerable network capacity in just sending acknowledgements.)
Thus, when transfer server 100 broadcasts the message, if one of clients 104 is off line because of, for example, a power failure, a network failure, or some other unforeseen circumstance, that disabled client does not receive the data. Moreover, to preserve the resources of transfer server 100, transfer server 100 broadcasts the data only once and subsequently deletes the data to save its disk space. Thus, if a disabled client misses the single broadcast, the client has lost the data forever. Furthermore, even if the data is stored in a directory as with the traditional point-to-point transmissions described above, when the client comes back on line, it has no way of determining which or how many data messages it has missed. Thus, a client is left with incomplete data, thereby compromising its performance.